When you shop for an air conditioner, heat pump or furnace, every quote carries a few letters and a number: SEER2, EER2, HSPF2, AFUE. Each one answers the same question: how much heating or cooling you get for the energy you pay for. Higher is more efficient in every case. What matters is which rating applies to which equipment, and how much the difference is actually worth in your home.
The ratings at a glance
| Rating | Equipment | What it measures |
|---|---|---|
| SEER2 | Air conditioners, heat pumps in cooling | Cooling output over a modeled season per unit of electricity |
| EER2 | Air conditioners, heat pumps in cooling | Cooling efficiency at one hot condition, 95°F outdoors |
| HSPF2 | Heat pumps in heating | Heating output over a modeled season per unit of electricity |
| AFUE | Gas and oil furnaces, boilers | Share of the fuel’s energy that becomes heat over a year |
Why the numbers changed in 2023
Since January 1, 2023, air conditioners and heat pumps in the US have been rated under an updated federal test procedure, and the ratings carry a “2”: SEER2, EER2 and HSPF2. The main change is that the new test assumes the air resistance of real ductwork, where the old one assumed very little. The blower has to work harder under those conditions, so the same unit scores lower.
Two things follow:
- SEER2 is lower than the old SEER for the same equipment, by roughly 4 to 5 percent on a typical ducted split system. A 14.3 SEER2 unit is roughly equivalent to an old 15 SEER unit.
- HSPF2 drops further below the old HSPF, because the heating part of the test changed as well.
So never compare a SEER2 figure on a new quote with a SEER figure on an old label. Compare SEER2 with SEER2, and HSPF2 with HSPF2.
SEER2: seasonal cooling efficiency
SEER2 (seasonal energy efficiency ratio) is the cooling a system delivers over a modeled cooling season, divided by the electricity it uses. Because it averages performance across a range of outdoor temperatures, it is closer to how an air conditioner really runs than a single test point.
Higher SEER2 usually comes from larger coils, more efficient fan motors and compressors that can slow down. Single-stage units run at full output or not at all; two-stage units have a low and a high setting; variable-speed (inverter) units adjust in small steps.
A rating belongs to a matched system: a specific outdoor unit with a specific indoor coil or air handler, and sometimes a specific furnace. Pair the same outdoor unit with a different coil and the rating changes. Ask for the rating of the exact combination in your quote.
EER2: efficiency on a hot afternoon
EER2 (energy efficiency ratio) is measured at one condition: 95°F outdoors. It tells you how the system performs at the peak of a heat wave rather than across the season. Two units with the same SEER2 can have different EER2s, and the gap between the two numbers is often wider on variable-speed units, because their biggest gains come at part load.
The US sets regional minimums for central air conditioners, and California is in the Southwest region, where a new central AC has to meet both a SEER2 minimum and an EER2 minimum. Your installer should quote a matched system that meets both.
HSPF2: heat pump heating efficiency
HSPF2 (heating seasonal performance factor) is the heat a heat pump delivers over a modeled heating season, divided by the electricity it uses, including the backup electric heat it is expected to need. A heat pump moves heat from outside instead of making it, so it delivers more heat than the electricity it consumes. That is why HSPF2 numbers sit well above anything plain electric resistance heat could reach.
Heat pumps carry both ratings: SEER2 for cooling and HSPF2 for heating. In a home that needs heat on more days than cooling, the HSPF2 is often the rating that drives the bill. The heat pump service page covers how these systems are set up and kept efficient.
AFUE: furnace efficiency
AFUE (annual fuel utilization efficiency) is the share of the fuel’s energy that becomes heat in the home over a year. The rest leaves through the vent. A 95% AFUE furnace turns about 95% of the gas into heat; about 5% goes up the flue.
| Furnace type | Typical AFUE |
|---|---|
| Old furnaces with a standing pilot and natural draft | 56–70% |
| Standard efficiency (non-condensing) | 80–83% |
| High efficiency (condensing) | 90–98% |
A condensing furnace gets its extra efficiency from a second heat exchanger that pulls so much heat out of the exhaust that water condenses from it. That is why it vents through plastic pipe and needs a condensate drain, and why moving from an 80% furnace to a condensing one can mean new venting and a drain line, part of planning a furnace installation.
AFUE has two blind spots: it does not count the electricity the blower uses, and it does not count heat lost from the ducts. A 95% furnace feeding leaky attic ducts can deliver less heat to the rooms than its rating suggests.
What should you buy?
Consider your usage. If you barely use the AC, paying for the top SEER2 tier may not make sense. If you cool many hours a year, higher efficiency pays off faster.
Do the math. A simple example on the old SEER scale: the difference between a 16 SEER and a 20 SEER air conditioner might save $100–200 a year. If the more efficient unit costs $1,000 more, that is a 5–10 year payback. Fewer cooling hours stretch the payback; more hours shorten it. Set that against how long you plan to stay in the house and how long the equipment is likely to run, which the guide on how long an HVAC system lasts covers.
Don’t overlook installation. Ratings come from a lab. In your house, the refrigerant charge, the airflow, the duct leakage and the sizing decide how much of that rating you actually get. A properly installed 16 SEER system can outperform a poorly installed 20 SEER one. A careful AC installation checks all four.
Comfort counts too. Two-stage and variable-speed systems cost more, but they run quieter, longer cycles and remove moisture more steadily. For some households that matters more than the payback.
Efficiency ratings in a Hayward home
Hayward’s mild Mediterranean climate means fewer cooling hours than in hotter inland areas, and that stretches the payback on top-tier cooling efficiency. Winter nights in the 40s mean most homes need heat on more days than they need cooling, so for a heat pump look closely at the HSPF2, and for a furnace at the AFUE. Homes in the Hayward Hills, which run cooler and windier at night, lean further toward heating. In flatland homes with ducts in the attic or in the slab, sealing and insulating the ducts can matter as much as the rating on the new unit; the energy bill guide covers what you can do there.